Dissipative dynamics of a Harmonic Oscillator : A non-perturbative approach

Starting from a microscopic theory, we derive a master equation for a harmonic oscillator coupled to a bath of non-interacting oscillators. We follow a non-perturbative approach, proposed earlier by us for the free Brownian particle. The diffusion constants are calculated analytically and the positivity of the Master Equation is shown to hold above a critical temperature. We compare the long time behaviour of the average kinetic and potential energies with known thermodynamic results. In the limit of vainishing oscillator frequency of the system, we recover the results of the free Brownian particle.Comment: 7 pages, 3 figure

Periodicity of dynamical signatures of chaos in quantum kicked top

A host of dynamical measures of quantum correlations -- out-of-time ordered correlators, Loschmidt echo, generalized entanglement and observational entropy -- are useful to infer about the underlying classical chaotic dynamics in quantum regime. In this work, these measures are employed to analyse quantum kicked top with kick strength $k$. It is shown that, despite the differences in their definitions, these measures are periodic with $k$, and the periodicity depends on the number of spins represented by the kicked top. The periodic behaviour arises from the structure of the kicked top Floquet operator and spans the regime in which the corresponding classical dynamics is predominantly chaotic. This result can guide experiments towards the right choice of kick strengths to avoid repetitive dynamics.Comment: 11 pages, 8 figure

A new non-perturbative approach to Quantum Brownian Motion

Starting from the Caldeira-Leggett (CL) model, we derive the equation describing the Quantum Brownian motion, which has been originally proposed by Dekker purely from phenomenological basis containing extra anomalous diffusion terms. Explicit analytical expressions for the temperature dependence of the diffusion constants are derived. At high temperatures, additional momentum diffusion terms are suppressed and classical Langivin equation can be recovered and at the same time positivity of the density matrix(DM) is satisfied. At low temperatures, the diffusion constants have a finite positive value, however, below a certain critical temperature, the Master Equation(ME) does not satisfy the positivity condition as proposed by Dekker.Comment: 5 page

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First record of the one-stripe anthias Pseudanthias fasciatus (Kamohara,1954) (Perciformes: Serranidae: Anthiinae) from Indian waters

The anthiinid fish Pseudanthias fasciatus (Kamohara, 1954) is reported from Indian waters for the first time. These fishes were found in trawler bycatch landed at the Neendakara fisheries harbour (090 41’ 18.28" N lat. 760 33’ 05.89" E long.) near Kollam, Kerala, India. The morphometric and meristic characters of the two specimens obtained correspond with those of P. fasciatus published previously

Memory in a magnetic nanoparticle system: polydispersity and interaction effects

We report here a theory of relaxation of single domain magnetic nanoparticles, appropriate for analyzing measurements of Mossbauer spectra, magnetization response, and hysteretic coercivity. Our special focus of attention in the theoretical formulation is the presence of dipolar interaction between the magnetic particles. We discuss in detail the effect of interaction as well as particle size distribution on the measured relaxation spectra and irreversible, nonequilibrium magnetization response in field-cooled and zero-field-cooled situations. Some of the memory effects, similar to those seen in spin glass systems, may be put to important device applications by tuning the interaction and the particle size

A method to quantitatively evaluate Hamaker constant using the jump-into-contact effect in Atomic Force microscopy

We find that the jump-into-contact of the cantilever in the atomic force microscope (AFM) is caused by an inherent instability in the motion of the AFM cantilever. The analysis is based on a simple model of the cantilever moving in a nonlinear force field. We show that the jump-into-contact distance can be used to find the interaction of the cantilever tip with the surface. In the specific context of the attractive van der Waals interaction, this method can be realized as a new method of measuring the Hamaker constant for materials. The Hamaker constant is determined from the deflection of the cantilever at the jump-into-contact using the force constant of the cantilever and the tip radius of curvature, all of which can be obtained by measurements. The results have been verified experimentally on a sample of cleaved mica, a sample of Si wafer with natural oxide and a silver film, using a number of cantilevers with different spring constants. We emphasize that the method described here is applicable only to surfaces that have van der Waals interaction as the tip-sample interaction. We also find that the tip to sample separation at the jump-into-contact is simply related to the cantilever deflection at this point, and this provides a method to exactly locate the surface.Comment: 11 pages, 4 figures, 1 tabl

Whale shark landings in Uttar Kannada, Karnataka

The whale shark, Rhincodon typus Smith, 1828, has a circumglobal distribution in tropical and warm temperate seas. Since May 2003 it has been included under Appendix II of CITES, making the trade of this species regulated. The status of this species has since then been upgraded from “Data deficient” in 1996 to “Vulnerable” in 2000 by the IUCN. Currently it is protected under Schedule I Part II of the Wildlife Protection Act of India, 1972